Luminescent display device

ABSTRACT

A luminescent display device includes a substrate and a thin-film transistor above the substrate. The thin-film transistor includes a semiconductor layer, a gate insulating film on the semiconductor layer, a gate electrode on the gate insulating film, a source electrode, and a drain electrode. The luminescent display device further includes an interlayer insulating film on the gate electrode, a first capacitor electrode on the interlayer insulating film in a region above the gate electrode, and a luminescent element configured to be driven by a driver to produce luminescence. The driver includes the thin-film transistor, and the first capacitor electrode and the gate electrode constitute a capacitor.

NOTICE: More than one reissue application has been filed for the reissueof U.S. Pat. No. 9,461,102 B2. Reissue application Ser. No. 16/145,623is a reissue of U.S. Pat. No. 9,461,102 B2 and was filed on Sep. 28,2018. The present application is reissue of U.S. Pat. No. 9,461,102 B2and is a continuation reissue application of Reissue application Ser.No. 16/145,623.

CROSS REFERENCE TO RELATED APPLICATION

ThisU.S. patent application Ser. No. 13/012,294, which issued as U.S.Pat. No. 9,461,102 B2, is a continuation application of PCT ApplicationNo. PCT/JP2009/006415, filed on Nov. 27, 2009, designating the UnitedStates of America, the. Reissue application Ser. No. 16/145,623 is areissue of U.S. Pat. No. 9,461,102 B2 and was filed on Sep. 28, 2018.The present application is a Reissue Application of U.S. Pat. No.9,461,102 B2, and is a continuation reissue application of Reissueapplication Ser. No. 16/145,623. The disclosure of whicheach of theabove-identified applications, including the specification, drawings,and claims, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to luminescent display devices, andparticularly to an active-matrix luminescent display device whichincludes a luminescent element and a driving circuit having a capacitorand a thin-film transistor.

2. Description of the Related Art

Conventionally, there is an active development of luminescent displaydevices, such as organic electroluminescent elements (hereinafterabbreviated as organic EL elements), in which luminescent elements thatcontrol the luminance using an electric current are two-dimensionallyarranged. In particular, there is an ongoing development ofactive-matrix luminescent display devices in which pixel circuits arearranged which include, for each luminescent element, a driving circuitfor driving the luminescent element.

The driving circuit generally includes: a switching transistor whichselects a pixel for producing luminescence; a driving transistor whichdrives a luminescent element; and a capacitor. The driving circuitincludes, for example, a capacitor which holds a voltage for determiningan amount of a current passed by the driving transistor (see PatentLiterature 1: Japanese Unexamined Patent Application Publication No.2006-330736).

FIG. 1 shows the layout of a luminescent pixel 700 included in aconventional luminescent display device disclosed in PatentLiterature 1. As shown in FIG. 1, the luminescent pixel 700 is wiredwith a signal line 705, a scanning line 706, and a power line 707.Further, the luminescent pixel 700 includes a switching transistor 701,a capacitor 702, a driving transistor 703, and a luminescent element704. The luminescent element 704 is formed in the luminescent region ofthe luminescent pixel 700, whereas the switching transistor 701, thecapacitor 702, and the driving transistor 703 are formed in the drivingcircuit region.

SUMMARY OF THE INVENTION

With the above conventional technique, however, a region dedicated tothe capacitor is formed, thereby causing a problem that when the numberof capacitors or the capacitor area increases, the region for formingother elements becomes smaller, resulting in less design flexibility.

For example, as in the luminescent display device of Patent Literature 1shown in FIG. 1, most of the driving circuit region is occupied by thecapacitor 702. Therefore, in the case of forming a capacitor 702 whichoccupies a larger area or in the case of forming another capacitor, theregion for forming the driving transistor 703 and the switchingtransistor 701 becomes smaller. Alternatively, the luminescent regionbecomes smaller, leading to an increase in the density of the currentflowing in the luminescent element, thereby reducing the lifetime of theluminescent element.

In view of the above, the present invention has been conceived to solvethe above conventional problem, and it is an object of the presentinvention to provide a luminescent display device with higher designflexibility by forming a capacitor without a region dedicated to thecapacitor or a new region dedicated to the capacitor.

In order to achieve the above object, the luminescent display deviceaccording to an aspect of the present invention is a luminescent displaydevice including: a substrate; a thin-film transistor which is formedabove the substrate and includes: a semiconductor layer having a channelregion, a source region, and a drain region; a gate insulating filmformed on the semiconductor layer; a gate electrode formed on the gateinsulating film; and a source electrode and a drain electrode which areelectrically connected to the source region and the drain region of thesemiconductor layer, respectively; an interlayer insulating film formedon the gate electrode; a luminescent element which is driven by adriving circuit to produce luminescence, the driving circuit includingthe thin-film transistor; and a first capacitor electrode formed on theinterlayer insulating film in a region above the gate electrode, whereinthe first capacitor electrode and the gate electrode constitute a firstcapacitor.

According to the present invention, it is possible to provide aluminescent display device with higher design flexibility by forming acapacitor without a region dedicated to the capacitor or a new regiondedicated to the capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the invention. In the Drawings:

FIG. 1 shows the layout of a pixel included in a conventionalluminescent display device;

FIG. 2 is a block diagram showing an example structure of a luminescentdisplay device according to Embodiment 1;

FIG. 3 shows a circuit structure of a luminescent pixel included in adisplay unit according to Embodiment 1;

FIG. 4 shows an example layout of a luminescent pixel according toEmbodiment 1;

FIG. 5 shows a cross-sectional view of a luminescent pixel according toEmbodiment 1;

FIG. 6 shows a circuit structure of a luminescent pixel according to avariation of Embodiment 1;

FIG. 7 shows a cross-sectional view of a luminescent pixel according toa variation of Embodiment 1;

FIG. 8 shows a circuit structure of a luminescent pixel according toanother variation of Embodiment 1;

FIG. 9 shows a cross-sectional view of a luminescent pixel according toanother variation of Embodiment 1;

FIG. 10 shows a circuit structure of a luminescent pixel included in adisplay unit according to Embodiment 2;

FIG. 11 shows an example layout of a luminescent pixel according toEmbodiment 2;

FIG. 12 shows a cross-sectional view of a luminescent pixel according toEmbodiment 2;

FIG. 13 is an external view of a television set which includes aluminescent display device according to the present invention; and

FIG. 14 shows an example layout of a luminescent pixel in anothervariation of a luminescent display device according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Hereinafter, embodiments of the luminescent display device according tothe present invention are described with reference to the drawings.

The luminescent display device according to an aspect of the presentinvention is a luminescent display device including: a substrate; athin-film transistor which is formed above the substrate and includes: asemiconductor layer having a channel region, a source region, and adrain region; a gate insulating film formed on the semiconductor layer;a gate electrode formed on the gate insulating film; and a sourceelectrode and a drain electrode which are electrically connected to thesource region and the drain region of the semiconductor layer,respectively; an interlayer insulating film formed on the gateelectrode; a luminescent element which is driven by a driving circuit toproduce luminescence, the driving circuit including the thin-filmtransistor; and a first capacitor electrode formed on the interlayerinsulating film in a region above the gate electrode, wherein the firstcapacitor electrode and the gate electrode constitute a first capacitor.

With this, the gate electrode of the thin-film transistor is used notonly simply as the gate electrode but also as one of two electrodesconstituting the capacitor. Thus, the capacitor can be formed above thethin-film transistor to overlap with the thin-film transistor, enablingefficient use of the pixel space. As a result, a complex driving circuitwhich includes multiple thin-film transistors and multiple capacitorscan be formed in a region having a limited area. It is to be noted thatthe structure of the present invention can be applied to a capacitor forholding the gate voltage, as well as a capacitor for holding a thresholdvoltage Vth in the driving circuit.

Further, the luminescent display device may include a plurality of firstcapacitor electrodes including the first capacitor electrode, whereineach of the plurality of first capacitor electrodes and the gateelectrode may constitute the first capacitor.

Furthermore, the first capacitor electrode and one of the sourceelectrode and the drain electrode may form one layer, and the one of thesource electrode and the drain electrode may be electrically connectedto the first capacitor electrode.

With this, the other one of the two electrodes constituting thecapacitor and one of the source electrode and the drain electrode can beformed in one process.

Moreover, the luminescent element may be electrically connected to oneof the source electrode and the drain electrode, the thin-filmtransistor may be a driving transistor which supplies a driving currentto the luminescent element, and the first capacitor may be a capacitorfor setting a value of a current flowing in the driving transistor.

This makes it possible to form, in the driving circuit, the capacitorfor setting the value of the driving current flowing in the drivingtransistor, while efficiently using the pixel space.

Further, the thin-film transistor may be a switching transistor whichdetermines timing of supplying a driving current to the luminescentelement, and the first capacitor may be a capacitor for initializing acapacitor used for setting a value of the driving current.

With this, one of the capacitor electrodes of the capacitor can be usedalso as, not only the gate electrode of the driving transistor, but alsothe gate electrode of the switching transistor. Therefore, it ispossible to arrange a greater number of thin-film transistors andcapacitors by efficiently using the limited pixel space.

Furthermore, the luminescent display device may further include a secondcapacitor, wherein the second capacitor may be electrically connected tothe first capacitor in parallel.

With this, in addition to the first capacitor, the second capacitor isalso formed in parallel, making it possible to increase the capacitanceby the capacitance of the second capacitor.

Further, the second capacitor may include an upper second capacitorelectrode and a lower second capacitor electrode, one of the uppersecond capacitor electrode and the lower second capacitor electrode maybe electrically connected to the gate electrode, and the other one ofthe upper second capacitor electrode and the lower second capacitorelectrode may be electrically connected to one of the source electrodeand the drain electrode.

This makes it possible to increase the capacitance by the capacitance ofthe second capacitor, allowing for stability in the voltage even whenthere is a leak current, and thus crosstalk can be reduced.

Furthermore, the upper second capacitor electrode and one of the sourceelectrode and the drain electrode may form one layer, the lower secondcapacitor electrode and the gate electrode may form one layer, and thefirst capacitor electrode may be electrically connected to the uppersecond capacitor electrode and to one of the source electrode and thedrain electrode.

This makes it possible to form, as one layer, first ones of thecapacitor electrodes constituting the first capacitor and the secondcapacitor, and to form, as another layer, second ones of the capacitorelectrodes constituting the first capacitor and the second capacitor,thereby enabling reduction in the number of manufacturing processes.

Moreover, an area of a lower surface of the first capacitor electrode,which is part of the first capacitor, in the region above the gateelectrode may be 30% to 100% of an area of an upper surface of the gateelectrode.

Further, the semiconductor layer may be made of polysilicon.

Furthermore, the luminescent element may be an organicelectroluminescent element.

Furthermore, a capacitance of the first capacitor may be 0.1 to 10 pF.

Moreover, the luminescent display device may be a top-emissionluminescent display device, and the luminescent element may be formed ina layer above the first capacitor electrode.

Moreover, the luminescent display device may be a bottom-emissionluminescent display device, and the thin-film transistor and the firstcapacitor may be formed in a region other than a luminescent region inwhich the luminescent element is formed.

Embodiment 1

The luminescent display device according to Embodiment 1 includes adriving transistor and a capacitor, and the gate electrode of thedriving transistor is one of two capacitor electrodes constituting thecapacitor. Thus, the capacitor is formed in a region which is above thedriving transistor and which includes the gate electrode of the drivingtransistor.

FIG. 2 is a block diagram showing an electrical structure of aluminescent display device 10 according to Embodiment 1. The luminescentdisplay device 10 in FIG. 2 at least includes a control circuit 20, ascanning line driving circuit 40, a signal line driving circuit 50, anda display unit 60.

FIG. 3 shows a circuit structure of a luminescent pixel 100 included inthe display unit 60 according to Embodiment 1. The luminescent pixel 100in FIG. 3 includes a switching transistor 101, a capacitor 102, adriving transistor 103, an organic EL element 104, a signal line 105, ascanning line 106, a higher-voltage-side power line 107, and alower-voltage-side power line 108.

First, the following describes the connection relationships andfunctions of the structural elements shown in FIG. 2.

The control circuit 20 has a function to control the scanning linedriving circuit 40 and the signal line driving circuit 50. The controlcircuit 20 outputs a video signal received from outside, to the signalline driving circuit 50, and controls the operational timing of thescanning line driving circuit 40 according to the operation of thesignal line driving circuit 50.

The scanning line driving circuit 40 is connected to the scanning line106, and has a function to output a scan signal to the scanning line 106to control between the conductive state (ON state) and thenon-conductive state (OFF state) of the switching transistor 101included in the luminescent pixel 100.

The signal line driving circuit 50 is connected to the signal line 105,and has a function to apply, to the luminescent pixel 100, a signalvoltage based on a video signal.

The display unit 60 includes a plurality of luminescent pixels 100 whichare two-dimensionally arranged, and displays an image based on the videosignal input to the luminescent display device 10 from outside.

Next, the following describes the connection relationships and functionsof the structural elements shown in FIG. 3.

The switching transistor 101 is an example of a switching element inwhich the gate is connected to the scanning line 106, one of the sourceand the drain is connected to the signal line 105, and the other one ofthe source and the drain is connected to a capacitor electrode 102a ofthe capacitor 102. The switching transistor 101 has a function todetermine timing of applying the signal voltage at the signal line 105to the capacitor electrode 102a of the capacitor 102. The switchingtransistor 101 is, for example, an n-type thin-film transistor (n-typeTFT), but may be a p-type TFT.

The capacitor 102 is an example of the first capacitor and includes twocapacitor electrodes 102a and 102b. The capacitor electrode 102a isconnected to the gate of the driving transistor 103, whereas thecapacitor electrode 102b is connected to the higher-voltage-side powerline 107. The capacitor 102 holds a charge corresponding to the signalvoltage supplied from the signal line 105. In other words, the capacitor102 is an example of a capacitive element used for setting a value of adriving current supplied to the organic EL element 104. For example, thecapacitor 102 has a function to cause the driving transistor 103 tosupply the driving current to the organic EL element 104 even when theswitching transistor 101 is switched to the OFF state, until anothersignal voltage is applied.

The driving transistor 103 is an example of a driving element in whichthe source is connected to the higher-voltage-side power line 107 andthe drain is connected to the anode of the organic EL element 104. Thedriving transistor 103 coverts a voltage corresponding to a signalvoltage applied between the gate and the source into a source-draincurrent corresponding to the applied signal voltage. The drivingtransistor 103 then supplies the source-drain current to the organic ELelement 104 as the driving current. The driving transistor 103 is ap-type thin-film transistor (p-type TFT), for example.

The organic EL element 104 is an example of a luminescent element whichis driven to produce luminescence by a driving circuit which includes athin-film transistor such as the driving transistor 103. In the organicEL element 104, the anode is connected to the drain of the drivingtransistor 103, and the cathode is connected to the lower-voltage-sidepower line 108. The organic EL element 104 produces luminescence whenthe driving transistor 103 passes the driving circuit through theorganic EL element 104. The luminescence intensity is controlled by amagnitude of the driving current; in other words, the signal voltage.

The signal line 105 is connected to the signal line driving circuit 50and to each of luminescent pixels in the pixel column that includes theluminescent pixel 100, and has a function to supply a signal voltagethat determines the luminescence intensity. It is to be noted that theluminescent display device 10 includes the same number of signal lines105 as the number of pixel columns.

The scanning line 106 is connected to the scanning line driving circuit40 and to each of luminescent pixels in the pixel row that includes theluminescent pixel 100. With this, the scanning line 106 has a functionto supply a signal indicating timing of applying the signal voltage toeach of the luminescent pixels in the pixel row that includes theluminescent pixel 100. It is to be noted that the luminescent displaydevice 10 includes the same number of scanning lines 106 as the numberof pixel rows.

Although not shown in FIG. 2 or FIG. 3, each of the higher-voltage-sidepower line 107 and the lower-voltage-side power line 108 is alsoconnected to other luminescent pixels and to a voltage source. Thepotential difference between a voltage source VDD to which thehigher-voltage-side power line 107 is connected and a voltage source VEEto which the lower-voltage-side power line 108 is connected has amagnitude which allows passage of a current which is sufficient to causethe organic EL element 104 to produce luminescence. It is to be notedthat the lower-voltage-side power line 108 may be grounded.

As shown in the above structure, the luminescent display device 10according to Embodiment 1 includes the display unit 60 in which aplurality of luminescent pixels 100 are two-dimensionally arranged. Thedisplay unit 60 displays video as the organic EL elements 104 in theluminescent pixels 100 produce luminescence at the luminescenceintensity according to the signal voltages.

The following describes the positional relationships between theelements included in the luminescent pixel 100 according to Embodiment1.

FIG. 4 shows an example layout of the luminescent pixel 100 according toEmbodiment 1.

As shown in FIG. 4, the luminescent pixel 100 can be separated into adriving circuit region 110 and a luminescent region 120. In theluminescent region 120, the organic EL element 104 is formed whichproduces luminescence according to the signal voltage supplied from thesignal line 105. It is to be noted that the luminescent display device10 according to Embodiment 1 is assumed as a bottom-emission luminescentdisplay device. To be more specific, luminescence produced by theorganic EL element 104 is directed toward the bottom surface of thesubstrate. In other words, the display surface of the display unit 60 ison the bottom surface side of the substrate.

The driving circuit region 110 is the region of the luminescent pixel100 excluding the luminescent region 120, and is a region in which thedriving circuit driving the organic EL element 104 is formed. In thedriving circuit region 110, the switching transistor 101, the capacitor102, and the driving transistor 103 are formed.

FIG. 5 shows a cross-sectional view of the luminescent pixel 100according to Embodiment 1. More specifically, FIG. 5 schematically showsa cross section A-A of the luminescent pixel 100 shown in FIG. 4. Thecross section A-A is a cross section showing the positional relationshipbetween the capacitor 102 and the driving transistor 103. Forsimplicity, FIG. 5 does not show the signal line 105 and thehigher-voltage-side power line 107.

As shown in FIG. 5, the driving transistor 103 is formed on a substrate210. The driving transistor 103 includes a semiconductor layer 220, agate insulating film 230, a gate electrode 103g, a source electrode103s, and a drain electrode 103d. Further, the capacitor 102 includesthe capacitor electrode 102b, an interlayer insulating film 240, and thecapacitor electrode 102a which functions also as the gate electrode103g. Further, a planarizing film 250 is formed on the capacitor 102.

The substrate 210 is, for example, a transparent substrate such as glassor quartz. The substrate 210 may be a flexible substrate such as aplastic. In the case of a top-emission luminescent display device, thesubstrate 210 may be a semiconductor substrate such as a siliconsubstrate, or a compound semiconductor substrate made with a compoundsemiconductor such as a nitride semiconductor.

Although it has been described above that the driving transistor 103 isformed on the substrate 210, it may be formed above the substrate 210.For example, a buffer layer may be formed on the substrate 210 and thedriving transistor 103 may be formed on the buffer layer.

The semiconductor layer 220 is a semiconductor layer formed on thesubstrate 210 and includes a channel region 221, a source region 222,and a drain region 223. For example, the semiconductor layer 220 is madewith a doped inorganic semiconductor such as polysilicon,microcrystalline silicon, or amorphous silicon, or an organicsemiconductor.

It is to be noted that the driving transistor 103 is a p-type TFT, andthus, holes mainly contribute to the conduction in the channel region221. That is to say, the above-described driving current flows as theholes move from the source region 222 to the drain region 223 accordingto voltages applied to the source electrode 103s, the drain electrode103d, and the gate electrode 103g.

The gate insulating film 230 is, for example, a film having insulatingproperties, such as a silicon oxide film (SiO_(x)). In the example shownin FIG. 5, the gate insulating film 230 is formed on the entire surfaceof the substrate 210 to cover the semiconductor layer 220, andthrough-holes are formed in the regions above the source region 222 andthe drain region 223. The gate insulating film 230 is sufficient as longas it is formed on the channel region 221 at least.

The gate electrode 103g is a metal electrode formed on the gateinsulating film 230. For example, the gate electrode 103g has asingle-layer structure of a metal such as molybdenum or tungsten, analloy of molybdenum and tungsten, or polysilicon, or has a laminatedstructure of polysilicon, and titanium and tungsten, or the like. It isto be noted that the gate electrode 103g is connected to the source ordrain of the switching transistor 101 (not shown in FIG. 5). The mostsignificant feature of the present invention is that the gate electrode103g also functions as the capacitor electrode 102a of the capacitor102.

The source electrode 103s is formed on the source region 222, and ismade of a metal such as aluminum or copper or has a laminated structureof metals such as aluminum and molybdenum, for example. The sourceelectrode 103s is connected to the higher-voltage-side power line 107(not shown in FIG. 5). Further, as shown in FIG. 5, the source electrode103s is connected to the capacitor electrode 102b of the capacitor 102via the through-hole formed in the interlayer insulating film 240 and inthe gate insulating film 230.

The drain electrode 103d is formed on the drain region 223, and is madeof a metal such as aluminum or has a laminated structure of metals suchas aluminum and molybdenum, for example. The drain electrode 103d isconnected to the anode of the organic EL element 104 (not shown in FIG.5).

The interlayer insulating film 240 is formed on the gate electrode 103gand is made with, for example, a silicon nitride film (SiN_(x)), asilicon oxide film, or the like. In the example shown in FIG. 5, theinterlayer insulating film 240 is formed on the entire surface of thegate insulating film 230 to cover the gate electrode 103g, andthrough-holes are formed in the regions above the source region 222 andthe drain region 223. The interlayer insulating film 240 is sufficientas long as it is formed on the gate electrode 103g at least.

It is to be noted that the thickness of the interlayer insulating film240 is 100 to 1000 nm.

The capacitor electrode 102b is an example of the first capacitorelectrode and is formed on the interlayer insulating film 240 above thegate electrode 103g. Put it differently, the capacitor electrode 102b isformed on the interlayer insulating film 240 in the region above thegate electrode 103g. The capacitor electrode 102b, together with thegate electrode 103g that is the other capacitor electrode 102a,constitutes the capacitor 102. For example, the capacitor electrode 102bis made of a metal such as aluminum or copper, or has a laminatedstructure of metals such as aluminum and molybdenum. In this example,the capacitor electrode 102b is connected to the higher-voltage-sidepower line 107.

Further, the capacitor electrode 102b and the source electrode 103s formone layer and are connected to each other. More specifically, thecapacitor electrode 102b is connected to the source electrode 103s viathe through-hole formed in the interlayer insulating film 240.Preferably, the capacitor electrode 102b is made of the same material asthat of the source electrode 103s. This makes it possible to form thecapacitor electrode 102b and the source electrode 103s in the sameprocess, thereby achieving reduction in the number of processes.

The area of the lower surface of the capacitor electrode 102b in theregion above the gate electrode 103g, which is the capacitor electrode102a, is 30% to 100% of the area of the upper surface of the gateelectrode 103g. It is to be noted that the capacitor electrode 102b maybe larger than the gate electrode 103g. Further, the capacitance of thecapacitor 102 is 0.1 to 10 pF.

The planarizing film 250 is formed on the capacitor 102, and functionsas a protection film which protects the capacitor 102 and the drivingtransistor 103 and also functions as a planarizing film which planarizesthe upper surfaces of the capacitor 102 and the driving transistor 103.The planarizing film 250 is made with, for example, a silicon oxide film(SiO_(x)), a silicon nitride film (SiN_(x)), or the like.

As shown in the above structure, the capacitor 102 uses the gateelectrode 103g as one of the capacitor electrodes. In other words, thecapacitor 102 having the gate electrode 103g as the capacitor electrode102a is formed in the region above the driving transistor 103.

As shown in FIG. 4, this makes it possible to form the capacitor 102without a region, in the luminescent pixel 100, dedicated to thecapacitor 102. Therefore, it is possible to relatively flexibly designthe area of the capacitor 102 or design the arrangement of the drivingtransistor 103 and the switching transistor 101. Alternatively, anothercapacitor can be added to the driving circuit region 110. As describedabove, with the luminescent display device 10 according to Embodiment 1,it is possible to increase the design flexibility. With this, forexample, since the luminescent display device 10 according to Embodiment1 is a bottom-emission luminescent display device, it is possible toensure a wide area for the luminescent region 120, reduce the density ofthe current flowing in the organic EL element 104, and ensure a longerluminescence lifetime for the luminescent display device 10.

It is to be noted that the structure in which the capacitor is formedabove the driving transistor 103 as shown in the present embodiment canbe applied to a driving circuit other than the circuit shown in FIG. 3.More specifically, the structure according to the present embodiment canbe applied to a driving circuit having a circuit structure in which thegate of the driving transistor 103 is electrically connected to one oftwo capacitor electrodes constituting the capacitor. The followingdescribes some variations with reference to the drawings.

(Variation 1)

FIG. 6 shows a circuit structure of a luminescent pixel 300 according toa variation of Embodiment 1. The luminescent pixel 300 shown in FIG. 6includes switching transistors 101, 313, 314 and 315, the drivingtransistor 103, capacitors 311 and 312, the organic EL element 104, thesignal line 105, scanning lines 106, 316, 317 and 318, thehigher-voltage-side power line 107, the lower-voltage-side power line108, and a reference voltage power line 319. It is to be noted that thesame structural elements as that of the luminescent pixel 100 shown inFIG. 3 are given the same reference signs and the descriptions thereofare omitted below.

The switching transistor 313 is an example of a switching element inwhich the gate is connected to the scanning line 316, one of the sourceand the drain is connected to the reference voltage power line 319, andthe other one of the source and the drain is connected to one of thesource and the drain of the switching transistor 101. The switchingtransistor 313 has a function to initialize the gate potential of thedriving transistor 103, that is, a function to set the gate potential ofthe driving transistor 103 to a reference potential Vref.

To be more specific, the switching transistor 313 is turned on by ascanning signal supplied from the scanning line 316, and supplies thereference potential Vref to second electrodes of the capacitors. It isto be noted that the switching transistor 313 is an n-type TFT, forexample.

The switching transistor 314 is an example of a switching element inwhich the gate is connected to the scanning line 317, one of the sourceand the drain is connected to the gate of the driving transistor 103,and the other one of the source and the drain is connected to the drainof the driving transistor 103. The switching transistor 314 has afunction to detect a threshold voltage of the driving transistor 103.

More specifically, for example, the switching transistor 314 is turnedon by a scanning signal supplied from the scanning line 317, andshort-circuits the gate and the drain of the driving transistor 103.Accordingly, the threshold voltage of the driving transistor 103 isgenerated at the gate electrode of the driving transistor 103. Theswitching transistor 314 is an n-type TFT, for example.

The switching transistor 315 is an example of a switching element inwhich the gate is connected to the scanning line 318, one of the sourceand the drain is connected to the drain of the driving transistor 103,and the other one of the source and the drain is connected to the anodeof the organic EL element 104. The switching transistor 315 has afunction to determine timing of supplying the driving current to theorganic EL element 104.

More specifically, for example, the switching transistor 315 is turnedon by a scanning signal supplied from the scanning line 318, and whenthe driving transistor 103 is turned on while the switching transistor315 is on, the driving current is supplied to the organic EL element104. To put it differently, the driving current is not supplied to theorganic EL element 104 while the switching transistor 315 is off,regardless of the operation of the driving transistor 103. It is to benoted that the switching transistor 315 is an n-type TFT, for example.

The capacitor 311 includes two capacitor electrodes 311a and 311b. Thecapacitor electrode 311a is connected to the reference voltage powerline 319, whereas the capacitor electrode 311b is connected to one ofthe source and the drain of the switching transistor 101. The capacitorelectrode 311b is also connected to the gate of the driving transistor103 via the capacitor 312. The capacitor 311 holds a chargecorresponding to the signal voltage supplied from the signal line 105.

The capacitor 312 is an example of the first capacitor, and includes twocapacitor electrodes 312a and 312b. The capacitor electrode 312b isconnected to one of the source and the drain of the switching transistor101, whereas the capacitor electrode 312a is connected to the gate ofthe driving transistor 103. The capacitor 312 holds a chargecorresponding to the threshold voltage of the driving transistor 103.

The scanning lines 316, 317 and 318 are connected to the scanning linedriving circuit 40 and to each of luminescent pixels in the pixel columnthat includes the luminescent pixel 300. The scanning line 316 has afunction to supply a reference voltage for detecting the thresholdvoltage of the driving transistor 103 which is included in each of theluminescent pixels in the pixel row that includes the luminescent pixel300.

The scanning line 317 has a function to supply a signal indicatingtiming of detecting the threshold voltage of the driving transistor 103which is included in each of the luminescent pixels in the pixel rowthat includes the luminescent pixel 300. The scanning line 318 has afunction to supply: a signal indicating timing of supplying the drivingcurrent to the organic EL element 104 which is included in each of theluminescent pixels in the pixel row that includes the luminescent pixel300; and a signal indicating timing of detecting the threshold voltageof the driving transistor 103.

It is to be noted that the luminescent display device 10 includes thesame number of scanning lines 316, 317 and 318 as the number of pixelrows.

The reference voltage power line 319 is also connected to otherluminescent pixels and to a voltage source which supplies apredetermined reference voltage. With this, the potential at thereference voltage power line 319 is maintained at the referencepotential Vref.

FIG. 7 shows a partial cross-sectional view of the luminescent pixel 300according to Variation 1 of Embodiment 1. Specifically, FIG. 7 shows thestructure in which the capacitor 312 and the driving transistor 103 arearranged. It is to be noted that the cross-sectional structure of thedriving transistor 103 is the same as the cross-sectional structureshown in FIG. 5, and thus the description thereof is omitted below.

As shown in FIG. 7, the capacitor electrode 312b of the capacitor 312 isformed on the interlayer insulating film 240. The gate electrode 103gfunctions also as the capacitor electrode 312a of the capacitor 312.

The capacitor electrode 312b is an example of the first capacitorelectrode, and is not connected to the source electrode 103s or thedrain electrode 103d of the driving transistor 103. The capacitorelectrode 312b is connected to one of the source and the drain of theswitching transistor 101 and to the capacitor electrode 311b (not shownin FIG. 7).

As described above, the capacitor electrode 312b of the capacitor 311formed on the driving transistor 103 does not have to be connected toeach electrode of the driving transistor 103. That is to say, thestructure according to the present embodiment can be applied as long asone of the two electrodes constituting the capacitor is connected to thegate electrode 103g of the driving transistor 103.

(Variation 2)

FIG. 8 shows a circuit structure of a luminescent pixel 400 according toanother variation of Embodiment 1. The luminescent pixel 400 shown inFIG. 8 is different from the luminescent pixel 300 shown in FIG. 6 inthat the luminescent pixel 400 includes a capacitor 411 instead of thecapacitor 311 and a switching transistor 413 instead of the switchingtransistor 313. Hereinafter, the same structural elements as that of theluminescent pixel 300 shown in FIG. 6 are given the same reference signsand the descriptions thereof are omitted below.

The capacitor 411 is an example of the first capacitor, and includes twocapacitor electrodes 411a and 411b. The capacitor electrode 411a isconnected to the gate electrode 103g of the driving transistor 103,whereas the capacitor electrode 411b is connected to, for example, thehigher-voltage-side power line 107. The capacitor 411 holds a chargecorresponding to the signal voltage supplied from the signal line 105and to the threshold voltage of the driving transistor.

The switching transistor 413 is an example of a switching element inwhich the gate is connected to the scanning line 316, one of the sourceand the drain is connected to the higher-voltage-side power line 107,and the other one of the source and the drain is connected to one of thesource and the drain of the switching transistor 101 and to thecapacitor electrode 312b of the capacitor 312. The switching transistor413 has a function to initialize the capacitor 312 and the capacitor411.

More specifically, the switching transistor 413 performs theinitialization such that the capacitor 312 and the capacitor 411 holdthe threshold voltage of the driving transistor 103 when the switchingtransistor 413 is turned on by a scanning signal supplied from thescanning line 316, the potential at the capacitor electrode 312b of thecapacitor 312 is set to VDD, and the switching transistor 314 is turnedon by a scanning signal supplied from the scanning line 317. It is to benoted that the switching transistor 413 is an n-type TFT, for example.

FIG. 9 shows a cross-sectional view of the luminescent pixel 400according to Variation 2 of Embodiment 1. Specifically, FIG. 9 shows thestructure in which the capacitor 312, the capacitor 411, and the drivingtransistor 103 are arranged. It is to be noted that the cross-sectionalstructure of the driving transistor 103 is the same as thecross-sectional structure shown in FIG. 5, and thus the descriptionthereof is omitted below.

As shown in FIG. 9, the capacitor electrode 312b of the capacitor 312and the capacitor electrode 411b of the capacitor 411 are formed on theinterlayer insulating film 240. The gate electrode 103g functions alsoas the capacitor electrode 312a of the capacitor 312 and the capacitorelectrode 411a of the capacitor 411.

The capacitor electrode 411b is an example of the first capacitorelectrode. The capacitor electrode 411b and the source electrode 103s ofthe driving transistor 103 form one layer and are connected to eachother. More specifically, the capacitor electrode 411b is connected tothe source electrode 103s via the through-hole formed in the interlayerinsulating film 240.

It is to be noted that the capacitor electrode 312b, the capacitorelectrode 411b, and the source electrode 103s are preferably made of thesame material. This makes it possible to form the capacitor electrode312b, the capacitor electrode 411b, and the source electrode 103s in thesame process, thereby achieving reduction in the number of processes.

As described above, the luminescent display device 10 according toVariation 2 of Embodiment 1 includes a plurality of first capacitorelectrodes, and each of the plurality of first capacitor electrodes andthe gate electrode 103g constitute the first capacitor. Although theexamples shown in FIG. 8 and FIG. 9 have illustrated two first capacitorelectrodes, there may be three or more first capacitor electrodes formedon the interlayer insulating film 240 in the region above the gateelectrode 103g.

As described above, in the luminescent display device 10 according toEmbodiment 1 and the variations thereof, the first capacitor isconstituted by the gate electrode 103g of the driving transistor 103included in the driving circuit and the first capacitor electrode formedabove the gate electrode 103g. The first capacitor having such astructure can be used as, for example, a capacitive element for settinga value of the driving current supplied to the organic EL element 104.

This enables efficient use of the limited region within the luminescentpixel 100. That is to say, the design flexibility can be increased.Accordingly, the luminescent display device 10 according to the presentembodiment provides an advantageous effect of ensuring a wide region forthe luminescent region 120, for example.

It is to be noted that the luminescent display device 10 according toEmbodiment 1 may further include a second capacitor which iselectrically connected to the capacitor 102 in parallel. For example,the second capacitor includes an upper second capacitor electrode and alower second capacitor electrode. One of the upper second capacitorelectrode and the lower second capacitor electrode is connected to thegate electrode 103g, and the other one is electrically connected to oneof the source electrode 103s and the drain electrode 103d.

More specifically, the lower second capacitor electrode and the gateelectrode 103g may form one layer, and the upper second capacitorelectrode and an electrically-connected one of the source electrode 103sand the drain electrode 103d may form one layer. Here, the capacitorelectrode 102a of the capacitor 102 is electrically connected to theupper second capacitor electrode.

Embodiment 2

The luminescent display device according to Embodiment 2 includes aswitching transistor, a driving transistor, and a capacitor, and thegate electrode of the switching transistor is one of two capacitorelectrodes constituting the capacitor. Thus, the capacitor is formed inthe region above the switching transistor.

The luminescent display device according to Embodiment 2 is differentfrom the luminescent display device 10 according to Embodiment 1 incircuit structure of each luminescent pixel included in the display unitand in arrangement of elements constituting each luminescent pixel. Inother words, the luminescent display device according to Embodiment 2has the same electrical structure as that of the luminescent displaydevice 10 according to Embodiment 1 shown in FIG. 2. Thus, thedescription of the electrical structure of the luminescent displaydevice according to Embodiment 2 is omitted, and the followingdescription centers on the circuit structure of each luminescent pixeland on the arrangement of the elements constituting each luminescentpixel.

FIG. 10 shows a circuit structure of a luminescent pixel 500 included ina display unit according to Embodiment 2. The luminescent pixel 500 inFIG. 10 includes switching transistors 501, 506, 507 and 508, capacitors502 and 505, a driving transistor 503, an organic EL element 504, asignal line 509, scanning lines 510, 511, 512 and 513, ahigher-voltage-side power line 514, a lower-voltage-side power line 515,and a reference voltage power line 516.

The switching transistor 501 is an example of a switching element inwhich the gate is connected to the scanning line 510, one of the sourceand the drain is connected to the signal line 509, and the other one ofthe source and the drain is connected to a capacitor electrode 502a ofthe capacitor 502 and to the gate of the driving transistor 503. Theswitching transistor 501 has a function to determine timing of applyinga signal voltage at the signal line 509 to the capacitor electrode 502aof the capacitor 502. The switching transistor 501 is an n-type TFT, forexample.

The capacitor 502 is an example of the first capacitor corresponding tothe driving transistor 503, and includes two capacitor electrodes 502aand 502b. The capacitor electrode 502a is connected to the gate of thedriving transistor 503, whereas the capacitor electrode 502b isconnected to a capacitor electrode 505b of the capacitor 505 and to thesource or drain of the switching transistor 507. The capacitor 502 holdsa charge corresponding to the signal voltage supplied from the signalline 509 and to a threshold voltage of the driving transistor 503. Inother words, the capacitor 502 is an example of a capacitive element forsetting a value of a driving current supplied to the organic EL element504.

The driving transistor 503 is an example of a driving element in whichthe drain is connected to the higher-voltage-side power line 514, andthe source is connected to the anode of the organic EL element 504 viathe switching transistor 508. The driving transistor 503 coverts avoltage corresponding to a signal voltage applied between the gate andthe source into a source-drain current corresponding to that signalvoltage. The driving transistor 503 is an n-type TFT, for example.

The organic EL element 504 is an example of a luminescent element inwhich the anode is connected to the source of the driving transistor 503via the switching transistor 508, and the cathode is connected to thelower-voltage-side power line 515. The organic EL element 504 producesluminescence when the driving transistor 503 passes the driving circuitthrough the organic EL element 504.

The capacitor 505 is an example of the first capacitor corresponding tothe switching transistor 508, and includes two capacitor electrodes 505aand 505b. The capacitor electrode 505a is connected to the scanning line513, whereas the capacitor electrode 505b is connected to the capacitorelectrode 502b and to one of the source and the drain of the switchingtransistor 507. The capacitor 505 is an example of a capacitive elementfor adjusting the amount of voltage held by the capacitor 502 which is acapacitive element which holds a data voltage applied from the signalline 509.

The switching transistor 506 is an example of a switching element inwhich the gate is connected to the scanning line 511, one of the sourceand the drain is connected to the reference voltage power line 516, andthe other one of the source and the drain is connected to the gate ofthe driving transistor 503. The switching transistor 506 has a functionto apply a reference voltage Vref to the gate of the driving transistor503. It is to be noted that the switching transistor 506 is an n-typeTFT, for example.

The switching transistor 507 is an example of a switching element inwhich the gate is connected to the scanning line 512, one of the sourceand the drain is connected to the capacitor electrode 502b of thecapacitor 502, and the other one of the source and the drain isconnected to the source of the driving transistor 503. The switchingtransistor 507 has a function to disconnect the capacitor 502 and thesource of the driving transistor 503 when applying a signal voltage tothe capacitor 502. It is to be noted that the switching transistor 507is an n-type TFT, for example.

The switching transistor 508 is an example of a switching element inwhich the gate is connected to the scanning line 513, one of the sourceand the drain is connected to the source of the driving transistor 503,and the other one of the source and the drain is connected to the anodeof the organic EL element 504. The switching transistor 508 has afunction to determine timing of supplying the driving current to theorganic EL element 504. It is to be noted that the switching transistor508 is an n-type TFT, for example.

The signal line 509 is connected to the signal line driving circuit andto each of luminescent pixels in the pixel column that includes theluminescent pixel 500, and has a function to supply a signal voltagethat determines the luminescence intensity. It is to be noted that theluminescent display device according to Embodiment 2 includes the samenumber of signal lines 509 as the number of pixel columns.

The scanning lines 510, 511, 512 and 513 are connected to the scanningline driving circuit and to each of luminescent pixels in the pixel rowthat includes the luminescent pixel 500. The scanning line 510 has afunction to supply a signal indicating timing of applying the signalvoltage to each of the luminescent pixels in the pixel row that includesthe luminescent pixel 500.

The scanning line 511 has a function to supply a signal indicatingtiming of applying a reference voltage Vref to the gate of the drivingtransistor 503 in each of the luminescent pixels in the pixel row thatincludes the luminescent pixel 500. The scanning line 512 has a functionto supply a signal indicating timing of disconnecting the capacitor 502and the source of the driving transistor 503 in each of the luminescentpixels in the pixel row that includes the luminescent pixel 500. Thescanning line 513 has a function to supply a signal indicating timing ofsupplying the driving current to the organic EL element 504 in each ofthe luminescent pixels in the pixel row that includes the luminescentpixel 500.

It is to be noted that the luminescent display device according toEmbodiment 2 includes the same number of scanning lines 510, 511, 512and 513 as the number of pixel rows.

Although not shown in FIG. 10, the higher-voltage-side power line 514,the lower-voltage-side power line 515, and the reference voltage powerline 516 are each connected to other luminescent pixels and to a voltagesource. The potential difference between the voltage source to which thehigher-voltage-side power line 514 is connected and the voltage sourceto which the lower-voltage-side power line 515 is connected has amagnitude which allows a flow of a current sufficient for the organic ELelement 504 to produce luminescence. It is to be noted that thelower-voltage-side power line 515 may be grounded.

FIG. 11 shows an example layout of the luminescent pixel 500 accordingto Embodiment 2. The luminescent display device according to Embodiment2 is assumed as a top-emission luminescent display device. To be morespecific, the luminescence produced by the organic EL element 504 isdirected toward the top surface of the substrate. In other words, thedisplay surface of the display unit is on the top surface side of thesubstrate.

In the luminescent pixel 500, the luminescent region in which theorganic EL element 504 is formed is the same as the driving circuitregion. That is to say, the luminescent region is formed above thedriving circuit region.

As shown in FIG. 11, the driving transistor 503 and the capacitor 502are formed in the same region in the plane to overlap each other, andthe switching transistor 508 and the capacitor 505 are formed in thesame region in the plane to overlap each other. The structure accordingto the present embodiment can be applied to such a circuit structure asabove in which the gate of a thin-film transistor such as the drivingtransistor 503 or the switching transistor 508 is electrically connectedwith a capacitor electrode of a capacitor.

FIG. 12 shows a cross-sectional view of the luminescent pixel 500according to Embodiment 2. More specifically, FIG. 12 shows a structurein which the switching transistor 508, the capacitor 505, and theorganic EL element 504 are arranged.

It is to be noted that the structure of the switching transistor 508 isthe same as that of the driving transistor 103 shown in FIG. 7. To bemore specific, a substrate 610, a semiconductor layer 620, a gateinsulating film 630, an interlayer insulating film 640, a gate electrode508g, a source electrode 508s, and a drain electrode 508d which areshown in FIG. 12 correspond to the substrate 210, the semiconductorlayer 220, the gate insulating film 230, the interlayer insulating film240, the gate electrode 103g, the source electrode 103s, and the drainelectrode 103d which are shown in FIG. 7, respectively. Further, achannel region 621, a source region 622, and a drain region 623 includedin the semiconductor layer 620 correspond to the channel region 221, thesource region 222, and the drain region 223 included in thesemiconductor layer 220, respectively.

As shown in FIG. 12, the capacitor electrode 505b of the capacitor 505is an example of the first capacitor electrode, and the capacitorelectrode 505b and the source electrode 508s form one layer and areconnected to each other. It is to be noted that instead of beingconnected to the source electrode 508s, the capacitor electrode 505b maybe electrically connected to the drain electrode 508d.

Since the luminescent display device according to Embodiment 2 is atop-emission luminescent display device, the organic EL element 504 isformed in a layer above the capacitor 505. More specifically, as shownin FIG. 12, the organic EL element 504 is formed above the capacitor 505with a planarizing film 650 therebetween. The organic EL element 504includes an anode 504a, a luminescent layer 504b, and a transparentcathode 504c.

The planarizing film 650 is made with a silicon nitride film, forexample.

The anode 504a is a light-reflective electrode and is made of a metalsuch as aluminum, for example. The anode 504a has a function to reflectluminescence produced by the luminescent layer 504b. The anode 504a isthe anode electrode of the organic EL element 504, and is connected tothe source of the driving transistor 503 via the switching transistor508 as shown in FIG. 10.

The luminescent layer 504b is a luminescent layer which is formedbetween the anode 504a and the transparent cathode 504c which istransparent or semitransparent, and produces luminescence due torecombination of the holes and electrons injected from the anode 504aand the transparent cathode 504c, respectively. It is to be noted thatthe luminescent layer 504b may include a hole transport layer, a holeinjection layer, an electron transport layer, an electron injectionlayer, and so on.

The transparent cathode 504c is a light-transmissive electrode and ismade with a transparent conductive oxide film such as an indium tinoxide (ITO), for example. The transparent cathode 504c is the cathodeelectrode of the organic EL element 504, and is connected to thelower-voltage-side power line 515 as shown in FIG. 10.

As described above, with the luminescent display device according toEmbodiment 2, the capacitor 505 is constituted by the gate electrode508g of the switching transistor 508 included in the driving circuit andthe capacitor electrode 505b formed above the gate electrode 508g. Thecapacitor 505 having such a structure can be used as, for example, acapacitive element for: initializing a capacitive element for settingthe value of the driving current supplied to the organic EL element 504;and adjusting the amount of voltage to be held by the capacitive elementout of the data voltage applied from the signal line 509.

Thus, the structure of the present embodiment can be applied to adriving circuit having a circuit structure in which the gate electrodeof a switching transistor and one of the capacitor electrodes of acapacitor are electrically connected. As a result, it is possible toreduce the region dedicated to the capacitor, and thus the designflexibility of the driving circuit can be increased.

Although the luminescent display device according to the presentinvention has been described above based on some exemplary embodiments,the present invention is not intended to be limited to such embodiments.Those skilled in the art may arrive at many modifications to the aboveexemplary embodiments and at various embodiments implemented bycombining the structural elements of different embodiments withoutmaterially departing from the novel teachings and advantages of thepresent invention. Accordingly, all such modifications and embodimentsare intended to be included within the scope of the present invention.

For example, the present invention is applicable to a circuit having acircuit structure in which the gate of a thin-film transistor includedin a driving circuit is connected with one of the electrodes of acapacitor. Although the above embodiments have described the structurein which the gate of a driving transistor or a switching transistor isconnected with one of the electrodes of a capacitor, the circuitstructure and so on is not limited to the above description.

Further, the above embodiments have described the switching transistorsas the n-type transistors which are turned on when a positive voltage isapplied to the gate of the switching transistors. However, the sameadvantageous effect as that of the above-described embodiments can beprovided also by a video display device in which the switchingtransistors are p-type transistors and the polarity of the scanninglines is reversed. Furthermore, although the above description explainedthat the lower electrode is the anode and the upper electrode is thecathode, it may surely be that the lower electrode is the cathode andthe upper electrode is the anode.

Moreover, for example, the luminescent display device according to thepresent invention is built in a television set as shown in FIG. 13. Withthe built-in luminescent display device according to the presentinvention, it is possible to provide a television set capable ofhigh-precision image display that reflects video signals.

Furthermore, the luminescent display device according to the presentinvention may include a second capacitor which is electrically connectedin parallel with a first capacitor having the gate electrode of athin-film transistor as the lower electrode as described above.

FIG. 14 shows an example layout of a luminescent pixel in anothervariation of the luminescent display device according to the presentinvention. In FIG. 14, the same structural elements as that of theconventional luminescent display device shown in FIG. 1 are given thesame reference signs and the descriptions thereof are omitted below.

As shown in FIG. 14, the luminescent pixel 700 includes a firstcapacitor 708 and a capacitor 702 which is a second capacitor. The firstcapacitor 708 is formed on the driving transistor 703 and includes anupper electrode and a lower electrode. The lower electrode of the firstcapacitor 708 functions also as the gate electrode of the drivingtransistor 703. The capacitor 702 which is the second capacitor includesan upper second capacitor electrode and a lower second capacitorelectrode.

The upper electrode of the first capacitor 708 is electrically connectedto the upper second capacitor electrode of the capacitor 702. Morespecifically, as shown in FIG. 14, the upper electrode of the firstcapacitor 708, the upper second capacitor electrode of the capacitor702, the power line 707, and one of the source electrode and the drainelectrode of the driving transistor 703 form one layer, and the upperelectrode of the first capacitor 708 is electrically connected to theone of the source electrode and the drain electrode of the drivingtransistor 703.

The lower electrode of the first capacitor 708 functions as the gateelectrode of the driving transistor 703 as described above, and iselectrically connected to the lower second capacitor electrode of thecapacitor 702. More specifically, as shown in FIG. 14, the lower secondcapacitor electrode of the capacitor 702 and the gate electrode which isthe lower electrode of the first capacitor 708 form one layer and areelectrically connected.

The above structure makes it possible to efficiently use the regionabove the driving transistor 703 and to increase the capacity of thecapacitor 702.

INDUSTRIAL APPLICABILITY

The luminescent display device according to the present invention isapplicable to various display devices such as television sets, personalcomputers, and mobile phones.

What is claimed is:
 1. A luminescent display device, comprising: asubstrate; and a plurality of pixels above the substrate, each of thepixels including: a thin film transistor above the substrate, the thinfilm transistor including: a semiconductor layer comprising a channelregion, a source region, and a drain region; a source electrodeelectrically connected to the source region of the semiconductor layer;and a drain electrode electrically connected to the drain region of thesemiconductor layer; a lower electrode above the substrate, the lowerelectrode including a first portion and a second portion, the firstportion of the lower electrode being provided in a region in which thethin film transistor is provided, the first portion of the lowerelectrode comprising a gate electrode of the thin film transistor, thesecond portion of the lower electrode being provided in a region otherthan the region in which the thin-film transistor is provided the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film on thelower electrode; an upper electrode on the interlayer insulating film,the upper electrode including a first portion and a second portion, theupper electrode, including the first portion and the second portion,comprising one continuous layer, the first portion of the upperelectrode comprising a capacitor electrode directly above the gateelectrode, the first portion of the upper electrode further comprisingthe source electrode, the capacitor electrode and the source electrodebeing connected via a through-hole in the interlayer insulating film;and a luminescent element configured to be driven by a driver to produceluminescence, the driver including the thin film transistor, wherein thefirst portion of the upper electrode and the first portion of the lowerelectrode comprise a first capacitance, and the second portion of theupper electrode and the second portion of the lower electrode comprise asecond capacitance.
 2. The luminescent display device according to claim1, wherein an area of a lower surface of the first portion of the upperelectrode, in the region in which the thin film transistor is provided,is approximately 30% to approximately 100% of an area of an uppersurface of the gate electrode.
 3. The luminescent display deviceaccording to claim 1, wherein the semiconductor layer comprisespolysilicon.
 4. The luminescent display device according to claim 1,wherein the first capacitance is approximately 0.1 pF to approximately10 pF.
 5. The luminescent display device according to claim 1, whereinthe luminescent display device is a top-emission luminescent displaydevice, and the luminescent element is in a layer above the upperelectrode.
 6. The luminescent display device according to claim 1,wherein the luminescent display device is a bottom-emission luminescentdisplay device, and the thin-film transistor, the lower electrode, andthe upper electrode are in a region other than a luminescent region inwhich the luminescent element is disposed.
 7. The luminescent displaydevice according to claim 1, wherein the one continuous layer of theupper electrode includes the source electrode of the thin filmtransistor.
 8. The luminescent display device according to claim 7,further comprising: a power line connected to the one of the sourceelectrode and the drain electrode of the thin film transistor, whereinthe one continuous layer of the upper electrode further includes thepower line.
 9. A luminescent display device, comprising: a substrate;and a plurality of pixels above the substrate, each of the pixelsincluding: a thin film transistor above the substrate, the thin filmtransistor including: a semiconductor layer comprising a channel region,a source region, and a drain region; a source electrode electricallyconnected to the source region of the semiconductor layer; and a drainelectrode electrically connected to the drain region of thesemiconductor layer; a lower electrode above the substrate, the lowerelectrode including a first portion and a second portion, the firstportion of the lower electrode being provided in a region in which thethin film transistor is provided, the first portion of the lowerelectrode comprising a gate electrode of the thin film transistor, thesecond portion of the lower electrode being provided in a region otherthan the region in which the thin-film transistor is provided, the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film on thelower electrode; an upper electrode on the interlayer insulating film,the upper electrode including a first portion and a second portion, theupper electrode, including the first portion and the second portion,comprising one continuous layer, the first portion of the upperelectrode comprising a capacitor electrode directly above the gateelectrode, the first portion of the upper electrode further comprisingthe source electrode, the capacitor electrode and the source electrodebeing connected via a through-hole in the interlayer insulating film;and a luminescent element configured to be driven by a driver to produceluminescence, the driver including the thin film transistor, wherein thefirst portion of the upper electrode and the first portion of the lowerelectrode comprise a first capacitance, and the second portion of theupper electrode and the second portion of the lower electrode comprise asecond capacitance, and the first portion of the upper electrode,including the capacitor electrode, extends from the second portion ofthe upper electrode to be directly above the gate electrode, with theupper electrode not being above a first portion of the interlayerinsulating film that is between a second portion of the interlayerinsulating film and the through-hole in the interlayer insulating film,the second portion of the interlayer insulating film being between thegate electrode and a part of the first portion of the upper electrodewhich is directly above the gate electrode.
 10. The luminescent displaydevice according to claim 9, wherein an area of a lower surface of thefirst portion of the upper electrode, in the region in which the thinfilm transistor is provided, is approximately 30% to approximately 100%of an area of an upper surface of the gate electrode.
 11. Theluminescent display device according to claim 9, wherein thesemiconductor layer comprises polysilicon.
 12. The luminescent displaydevice according to claim 9, wherein the first capacitance isapproximately 0.1 pF to approximately 10 pF.
 13. The luminescent displaydevice according to claim 9, wherein the luminescent display device is atop-emission luminescent display device, and the luminescent element isin a layer above the upper electrode.
 14. The luminescent display deviceaccording to claim 9, wherein the luminescent display device is abottom-emission luminescent display device, and the thin-filmtransistor, the lower electrode, and the upper electrode are in a regionother than a luminescent region in which the luminescent element isdisposed.
 15. The luminescent display device according to claim 9,wherein the one continuous layer of the upper electrode includes thesource electrode of the thin film transistor.
 16. The luminescentdisplay device according to claim 15, further comprising: a power lineconnected to the one of the source electrode and the drain electrode ofthe thin film transistor, wherein the one continuous layer of the upperelectrode further includes the power line.
 17. A luminescent displaydevice, comprising: a substrate; and a plurality of pixels above thesubstrate, each of the pixels including: a thin film transistor abovethe substrate, the thin film transistor including: a semiconductor layercomprising a channel region, a source region, and a drain region; asource electrode configured to be electrically connected to the sourceregion of the semiconductor layer; and a drain electrode configured tobe electrically connected to the drain region of the semiconductorlayer; a lower electrode above the substrate, the lower electrodeincluding a first portion and a second portion, the first portion of thelower electrode being provided in a region in which the thin filmtransistor is provided, the first portion of the lower electrodecomprising a gate electrode of the thin film transistor, the secondportion of the lower electrode being provided in a region other than theregion in which the thin-film transistor is provided, the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film above thelower electrode; an upper electrode, contacting the interlayerinsulating film, which is configured to be electrically connected to oneof the source region and the drain region of the semiconductor layer viaa through-hole in the interlayer insulating film, the upper electrodeincluding a first portion and a second portion, the upper electrode,including the first portion and the second portion, comprising onecontinuous layer, the first portion of the upper electrode overlappingthe first portion of the lower electrode to form a first capacitance,the second portion of the upper electrode overlapping the second portionof the lower electrode to form a second capacitance; and a luminescentelement configured to be driven by a driver to produce luminescence, thedriver including the thin film transistor, wherein the first portion ofthe upper electrode extends from the second portion of the upperelectrode to overlap the first portion of the lower electrode to formthe first capacitance, with the upper electrode including a physicalseparation that is above the semiconductor layer and that is between thefirst portion of the upper electrode and a region of the through-holeabove the semiconductor layer.
 18. The luminescent display deviceaccording to claim 17, wherein an area of a lower surface of the firstportion of the upper electrode, in the region in which the thin filmtransistor is provided, is approximately 30% to approximately 100% of anarea of an upper surface of the gate electrode.
 19. The luminescentdisplay device according to claim 17, wherein the semiconductor layercomprises polysilicon.
 20. The luminescent display device according toclaim 17, wherein the first capacitance is approximately 0.1 pF toapproximately 10 pF.
 21. The luminescent display device according toclaim 17, wherein the luminescent display device is a top-emissionluminescent display device, and the luminescent element is in a layerabove the upper electrode.
 22. The luminescent display device accordingto claim 17, wherein a part of the upper electrode constitutes one ofthe source electrode and the drain electrode.
 23. The luminescentdisplay device according to claim 22, wherein the first portion of theupper electrode, the second portion of the upper electrode, and the partof the upper electrode which constitutes the one of the source electrodeand the drain electrode comprise one continuous layer.
 24. Theluminescent display device according to claim 23, wherein the firstportion of the upper electrode is connected to the one of the sourceelectrode and the drain electrode via the through-hole in the interlayerinsulating film.
 25. The luminescent display device according to claim17, wherein the first portion of the upper electrode is configured to beelectrically connected to one of the source electrode and the drainelectrode.
 26. The luminescent display device according to claim 25,wherein the first portion of the upper electrode, the second portion ofthe upper electrode, and the one of the source electrode and the drainelectrode comprise one continuous layer.
 27. The luminescent displaydevice according to claim 26, wherein the first portion of the upperelectrode is connected to the source electrode via the through-hole inthe interlayer insulating film.
 28. The luminescent display deviceaccording to claim 17, wherein the first portion of the upper electrode,the second portion of the upper electrode, and one of the sourceelectrode and the drain electrode comprise one continuous layer.
 29. Aluminescent display device, comprising: a substrate; and a plurality ofpixels above the substrate, each of the pixels including: a thin filmtransistor above the substrate, the thin film transistor including: asemiconductor layer comprising a channel region, a source region, and adrain region; a source electrode configured to be electrically connectedto the source region of the semiconductor layer; and a drain electrodeconfigured to be electrically connected to the drain region of thesemiconductor layer; a lower electrode above the substrate, the lowerelectrode including a first portion and a second portion, the firstportion of the lower electrode being provided in a region in which thethin film transistor is provided, the first portion of the lowerelectrode comprising a gate electrode of the thin film transistor, thesecond portion of the lower electrode being provided in a region otherthan the region in which the thin-film transistor is provided, the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film above thelower electrode; an upper electrode, contacting the interlayerinsulating film, which is configured to be electrically connected to oneof the source region and the drain region of the semiconductor layer viaa through-hole in the interlayer insulating film, the upper electrodeincluding a first portion and a second portion, the upper electrode,including the first portion and the second portion, comprising onecontinuous layer, the first portion of the upper electrode overlappingthe first portion of the lower electrode to form a first capacitance,the second portion of the upper electrode overlapping the second portionof the lower electrode to form a second capacitance; and a luminescentelement configured to be driven by a driver to produce luminescence, thedriver including the thin film transistor, wherein the first portion ofthe upper electrode extends from the second portion of the upperelectrode to overlap the first portion of the lower electrode to formthe first capacitance, with the upper electrode not being above a firstportion of the interlayer insulating film that is between a secondportion of the interlayer insulating film and the through-hole in theinterlayer insulating film, the second portion of the interlayerinsulating film being between the gate electrode and a part of the firstportion of the upper electrode which is directly above the gateelectrode.
 30. The luminescent display device according to claim 29,wherein an area of a lower surface of the first portion of the upperelectrode, in the region in which the thin film transistor is provided,is approximately 30% to approximately 100% of an area of an uppersurface of the gate electrode.
 31. The luminescent display deviceaccording to claim 29, wherein the semiconductor layer comprisespolysilicon.
 32. The luminescent display device according to claim 29,wherein the first capacitance is approximately 0.1 pF to approximately10 pF.
 33. The luminescent display device according to claim 29, whereinthe luminescent display device is a top-emission luminescent displaydevice, and the luminescent element is in a layer above the upperelectrode.
 34. The luminescent display device according to claim 29,wherein a part of the upper electrode constitutes one of the sourceelectrode and the drain electrode.
 35. The luminescent display deviceaccording to claim 34, wherein the first portion of the upper electrode,the second portion of the upper electrode, and the part of the upperelectrode which constitutes the one of the source electrode and thedrain electrode comprise one continuous layer.
 36. The luminescentdisplay device according to claim 35, wherein the first portion of theupper electrode is connected to the one of the source electrode and thedrain electrode via the through-hole in the interlayer insulating film.37. The luminescent display device according to claim 29, wherein thefirst portion of the upper electrode is configured to be electricallyconnected to one of the source electrode and the drain electrode. 38.The luminescent display device according to claim 37, wherein the firstportion of the upper electrode, the second portion of the upperelectrode, and the one of the source electrode and the drain electrodecomprise one continuous layer.
 39. The luminescent display deviceaccording to claim 38, wherein the first portion of the upper electrodeis connected to the source electrode via the through-hole in theinterlayer insulating film.
 40. The luminescent display device accordingto claim 29, wherein the first portion of the upper electrode, thesecond portion of the upper electrode, and one of the source electrodeand the drain electrode comprise one continuous layer.
 41. A luminescentdisplay device, comprising: a substrate; and a plurality of pixels abovethe substrate, each of the pixels including: a thin film transistorabove the substrate, the thin film transistor including: a semiconductorlayer comprising a channel region, a source region, and a drain region;a source electrode configured to be electrically connected to the sourceregion of the semiconductor layer; and a drain electrode configured tobe electrically connected to the drain region of the semiconductorlayer; a lower electrode above the substrate, the lower electrodeincluding a first portion and a second portion, the first portion of thelower electrode being provided in a region in which the thin filmtransistor is provided, the first portion of the lower electrodecomprising a gate electrode of the thin film transistor, the secondportion of the lower electrode being provided in a region other than theregion in which the thin-film transistor is provided, the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film above thelower electrode; an upper electrode contacting the interlayer insulatingfilm, the upper electrode including a first portion and a secondportion, the upper electrode, including the first portion and the secondportion, comprising one continuous layer, the first portion of the upperelectrode being above the gate electrode, a part of the upper electrodebeing connected to the source electrode, the part of the upper electrodeand the source electrode being connected via a through-hole in theinterlayer insulating film; and a luminescent element configured to bedriven by a driver to produce luminescence, the driver including thethin film transistor, wherein the first portion of the upper electrodeand the first portion of the lower electrode form a first capacitance ina region corresponding to the channel region, the second portion of theupper electrode and the second portion of the lower electrode form asecond capacitance in a region other than the region corresponding tothe channel region, and the first portion of the upper electrode extendsfrom the second portion of the upper electrode to be above the gateelectrode, with the upper electrode including a physical separation thatis above the semiconductor layer and that is between the first portionof the upper electrode and a region of the through-hole above thesemiconductor layer.
 42. The luminescent display device according toclaim 41, wherein an area of a lower surface of the first portion of theupper electrode, which is above the gate electrode, is approximately 30%to approximately 100% of an area of an upper surface of the gateelectrode.
 43. The luminescent display device according to claim 41,wherein the semiconductor layer comprises polysilicon.
 44. Theluminescent display device according to claim 41, wherein the firstcapacitance is approximately 0.1 pF to approximately 10 pF.
 45. Theluminescent display device according to claim 41, wherein theluminescent display device is a top-emission luminescent display device,and the luminescent element is in a layer above the upper electrode. 46.The luminescent display device according to claim 41, wherein the firstportion of the upper electrode, the second portion of the upperelectrode, and the source electrode comprise one continuous layer.
 47. Aluminescent display device, comprising: a substrate; and a plurality ofpixels above the substrate, each of the pixels including: a thin filmtransistor above the substrate, the thin film transistor including: asemiconductor layer comprising a channel region, a source region, and adrain region; a source electrode configured to be electrically connectedto the source region of the semiconductor layer; and a drain electrodeconfigured to be electrically connected to the drain region of thesemiconductor layer; a lower electrode above the substrate, the lowerelectrode including a first portion and a second portion, the firstportion of the lower electrode being provided in a region in which thethin film transistor is provided, the first portion of the lowerelectrode comprising a gate electrode of the thin film transistor, thesecond portion of the lower electrode being provided in a region otherthan the region in which the thin-film transistor is provided, the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film above thelower electrode; an upper electrode contacting the interlayer insulatingfilm, the upper electrode including a first portion and a secondportion, the upper electrode, including the first portion and the secondportion, comprising one continuous layer, the first portion of the upperelectrode being above the gate electrode, a part of the upper electrodebeing connected to the source electrode, the part of the upper electrodeand the source electrode being connected via a through-hole in theinterlayer insulating film; and a luminescent element configured to bedriven by a driver to produce luminescence, the driver including thethin film transistor, wherein the first portion of the upper electrodeand the first portion of the lower electrode form a first capacitance ina region corresponding to the channel region, the second portion of theupper electrode and the second portion of the lower electrode form asecond capacitance in a region other than the region corresponding tothe channel region, and the first portion of the upper electrode extendsfrom the second portion of the upper electrode to be above the gateelectrode, with the upper electrode not being above a first portion ofthe interlayer insulating film that is between a second portion of theinterlayer insulating film and the through-hole in the interlayerinsulating film, the second portion of the interlayer insulating filmbeing between the gate electrode and a part of the first portion of theupper electrode which is directly above the gate electrode.
 48. Theluminescent display device according to claim 47, wherein an area of alower surface of the first portion of the upper electrode, which isabove the gate electrode, is approximately 30% to approximately 100% ofan area of an upper surface of the gate electrode.
 49. The luminescentdisplay device according to claim 47, wherein the semiconductor layercomprises polysilicon.
 50. The luminescent display device according toclaim 47, wherein the first capacitance is approximately 0.1 pF toapproximately 10 pF.
 51. The luminescent display device according toclaim 47, wherein the luminescent display device is a top-emissionluminescent display device, and the luminescent element is in a layerabove the upper electrode.
 52. The luminescent display device accordingto claim 47, wherein the first portion of the upper electrode, thesecond portion of the upper electrode, and the source electrode compriseone continuous layer.
 53. A luminescent display device, comprising: asubstrate; and a plurality of pixels above the substrate, each of thepixels including: a thin film transistor above the substrate, the thinfilm transistor including: a semiconductor layer comprising a channelregion, a source region, and a drain region; a source electrodeelectrically connected to the source region of the semiconductor layer;and a drain electrode electrically connected to the drain region of thesemiconductor layer; a lower electrode above the substrate, the lowerelectrode including a first portion and a second portion, the firstportion of the lower electrode being provided in a region in which thethin film transistor is provided, the first portion of the lowerelectrode comprising a gate electrode of the thin film transistor, thesecond portion of the lower electrode being provided in a region otherthan the region in which the thin-film transistor is provided, the lowerelectrode, including the first portion and the second portion,comprising one continuous layer; an interlayer insulating film on thelower electrode; an upper electrode on the interlayer insulating film,the upper electrode including a first portion and a second portion, theupper electrode, including the first portion and the second portion,comprising one continuous layer, the first portion of the upperelectrode comprising a capacitor electrode directly above the gateelectrode, the first portion of the upper electrode further comprisingthe source electrode, the capacitor electrode and the source electrodebeing connected via a through-hole in the interlayer insulating film;and a luminescent element configured to be driven by a driver to produceluminescence, the driver including the thin film transistor, wherein thefirst portion of the upper electrode and the first portion of the lowerelectrode comprise a first capacitance, and the second portion of theupper electrode and the second portion of the lower electrode comprise asecond capacitance, and the first portion of the upper electrode,including the capacitor electrode, extends from the second portion ofthe upper electrode to be directly above the gate electrode, with theupper electrode including a physical separation that is above thesemiconductor layer and that is between the first portion of the upperelectrode and a region of the through-hole above the semiconductorlayer.
 54. The luminescent display device according to claim 53 whereinan area of a lower surface of the first portion of the upper electrode,in the region in which the thin film transistor is provided, isapproximately 30% to approximately 100% of an area of an upper surfaceof the gate electrode.
 55. The luminescent display device according toclaim 53, wherein the semiconductor layer comprises polysilicon.
 56. Theluminescent display device according to claim 53, wherein the firstcapacitance is approximately 0.1 pF to approximately 10 pF.
 57. Theluminescent display device according to claim 53, wherein theluminescent display device is a top-emission luminescent display device,and the luminescent element is in a layer above the upper electrode. 58.The luminescent display device according to claim 53, wherein theluminescent display device is a bottom-emission luminescent displaydevice, and the thin-film transistor, the lower electrode, and the upperelectrode are in a region other than a luminescent region in which theluminescent element is disposed.
 59. The luminescent display deviceaccording to claim 53, wherein the one continuous layer of the upperelectrode includes the source electrode of the thin film transistor. 60.The luminescent display device according to claim 59, furthercomprising: a power line connected to the one of the source electrodeand the drain electrode of the thin film transistor, wherein the onecontinuous layer of the upper electrode further includes the power line.